Comparisons of human uterine neoplasms with normal tissues have shown an increased rate of conversion of testosterone to its physiologically more active metabolite, dihydrotestosterone. In addition to these in vitro investigations, we have also identified a saturable cytoplasmic binding protein in both normal and neoplastic tissues. The androgen receptor concentrations are also elevated in the uterine neoplasms. The 5 alpha-reduction of testosterone and the specific binding of dihydrotestosterone constitute two important steps thought to be necessary for androgens to elicit tissue response. Furthermore, the elevated levels of both of these phenomena in the neoplasms studied suggest a physiologically significant role for androgens in uterine neoplastic disease.